﻿// Jinx AJAX Framework
// Copyright (C) 2008 Blake Hegerle
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Core;
using Formality.FormalSystem.Parser;

namespace Formality.FormalSystem.Reasoning.FunctionSubstitution
{
    public static class VariableCaptureHelper
    {
        public static Set<Variable> FreeVariables(this Proposition P)
        {
            var FreeVars = new Set<Variable>();
            P.FreeVariables(FreeVars, new Set<string>());
            return FreeVars;
        }

        public static void FreeVariables(this Proposition P, Set<Variable> FreeVars, Set<string> BoundVars)
        {
            if (P.Type == PropType.Binder)
            {
                var Bound = new Binder(P).Variable.Name;

                BoundVars.Add(Bound);

                foreach (var Op in P.Operands)
                    Op.FreeVariables(FreeVars, BoundVars);

                BoundVars.Remove(Bound);
            }
            else
            {
                foreach (var V in P.Variables)
                {
                    if (BoundVars.Contains(V.Name) == false)
                        FreeVars.Add(V);
                }

                foreach (var Op in P.Operands)
                    Op.FreeVariables(FreeVars, BoundVars);
            }
        }
    }
}

